Methods and devices for improving image quality based on synthesized pixel values

ABSTRACT

An image processing method includes capturing an initial image of a subject based on a preset initial exposure value, capturing a compensatory image of the subject based on a preset compensatory exposure value greater than the initial exposure value, calculating a synthesized pixel value at a pixel coordinate position based on a pixel value of an initial pixel at the pixel coordinate position in the initial image and a pixel value of a compensatory pixel at the pixel coordinate position in the compensatory image, and generating a captured image based upon the synthesized pixel value.

CROSS-REFERENCE TO RELATED APPLICATION

This is a continuation application of International Application No.PCT/CN2014/079778, filed on Jun. 12, 2014, the entire contents of whichare incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to image processing and, in particular,to an image processing method, device, and camera.

BACKGROUND

The pursuit of high image quality has been a motivation in improvingmethods and devices for capturing digital images. The quality of adigital image is typically measured by signal-to-noise ratio (SNR). If auniform area is being captured, the pixel values within an ideal photoof the uniform area should be identical. However, digital cameras arenot ideal. Due to the noise introduced from electrical characteristicsof sensors, pixel values in a captured photo may have a Gaussian-likedistribution around a central value. The SNR may be used to measure anon-ideality in imaging a uniform area.

Conventional approaches for improving the SNR may comprise improving amanufacturing process of sensors in camera equipment so as to increasethe image quality, which is in nature equipment upgrading. Such approachmay improve image quality to a certain extent while significantlyincreasing cost to cameras.

SUMMARY

Embodiments of the present disclosure provide an image processingmethod, device, and camera that are capable of improving image qualityat a low cost.

In accordance with the present disclosure, there is provided an imageprocessing method including capturing an initial image of a subjectbased on a preset initial exposure value, capturing a compensatory imageof the subject based on a preset compensatory exposure value greaterthan the initial exposure value, calculating a synthesized pixel valueat a pixel coordinate position based on a pixel value of an initialpixel at the pixel coordinate position in the initial image and a pixelvalue of a compensatory pixel at the pixel coordinate position in thecompensatory image, and generating a captured image based upon thesynthesized pixel value.

In some embodiments, calculating the synthesized pixel value includesdetermining a weight value of the initial pixel and a weight value ofthe compensatory pixel, and performing a weighted averaging to calculatethe synthesized pixel value based on the pixel value and the weightvalue of the initial pixel and the pixel value and the weight value ofthe compensatory pixel.

In some embodiments, determining the weight value of the initial pixeland the weight value of the compensatory pixel includes detecting thepixel value of the compensatory pixel, determining the weight value ofthe compensatory pixel as a value ranging from 0 to 1, and determiningthe weight value of the initial pixel based upon the determined weightvalue of the compensatory pixel.

In some embodiments, determining the weight value of the initial pixeland the weight value of the compensatory pixel includes detecting thepixel value of the compensatory pixel, determining a variablecorresponding to the compensatory pixels as having a value 0 if thepixel value of the compensatory pixel is less than a preset threshold oras having a value 1 if the pixel value of the compensatory pixel is noless than the preset threshold, generating a binary image for thecompensatory image based upon the determined variable, determining theweight value of the compensatory pixel according to the binary image,and determining the weight value of initial pixel based upon thedetermined weight value of the compensatory pixel.

In some embodiments, the method further includes performing a smoothfiltering on the binary image to generate a smoothed binary image. Inthese embodiments, determining the weight value of the compensatorypixel according to the binary image includes determining the weightvalue of the compensatory pixel according to the smoothed binary image.

In some embodiments, the initial image and the compensatory image aremulti-channel images each having a plurality of pixel components foreach pixel. In these embodiments, calculating the synthesized pixelvalue includes performing a brightness value conversion based on presetconversion coefficients and pixel component values of the compensatorypixel to obtain a brightness value of the compensatory pixel,determining a weight value of the compensatory pixel based upon thedetermined brightness value, determining a weight value of the initialpixel according to the determined weight value of the compensatorypixel, performing a weighted averaging to obtain a synthesized pixelcomponent value for each of the pixel components based on the weightvalue and the pixel component value of the pixel component of theinitial pixel and the weight value and the pixel component value of thepixel component of the compensatory pixel, and determining thesynthesized pixel value based upon the obtained synthesized pixelcomponent value for each of the pixel components.

Also in accordance with the present disclosure, there is provided animage processing device including a processor and a memory storinginstructions that, when executed by the processor, cause the processorto obtain an initial image of a subject captured based on a presetinitial exposure value, obtain a compensatory image of the subjectcaptured based on a preset compensatory exposure value greater than theinitial exposure value, calculate a synthesized pixel value at a pixelcoordinate position based on a pixel value of an initial pixel at thepixel coordinate position in the initial image and a pixel value of acompensatory pixel at the pixel coordinate position in the compensatoryimage, and generate a captured image based upon the synthesized pixelvalue.

In some embodiments, the instructions further cause the processor todetermine a weight value of the initial pixel and a weight value of thecompensatory pixel, and perform a weighted averaging to calculate thesynthesized pixel value based on the pixel value and the weight value ofthe initial pixel and the pixel value and the weight value of thecompensatory pixel.

In some embodiments, the instructions further cause the processor todetect the pixel value of the compensatory pixel, determine the weightvalue of the compensatory pixel as a value ranging from 0 to 1, anddetermine the weight value of the initial pixel based upon thedetermined weight value of the compensatory pixel.

In some embodiments, the instructions further cause the processor todetect the pixel value of the compensatory pixel, determine a variablecorresponding to the compensatory pixels as having a value 0 if thepixel value of the compensatory pixel is less than a preset threshold oras having a value 1 if the pixel value of the compensatory pixel is noless than the preset threshold, generate a binary image for thecompensatory image based upon the determined variable, determine theweight value of the compensatory pixel according to the binary image,and determine the weight value of initial pixel based upon thedetermined weight value of the compensatory pixel.

In some embodiments, the instructions further cause the processor toperform a smooth filtering on the binary image to generate a smoothedbinary image, and determine the weight value of the compensatory pixelaccording to the smoothed binary image.

In some embodiments, the initial image and the compensatory image aremulti-channel images each having a plurality of pixel components foreach pixel. In these embodiments, the instructions further cause theprocessor to perform a brightness value conversion based on presetconversion coefficients and pixel component values of the compensatorypixel to obtain a brightness value of the compensatory pixel, determinea weight value of the compensatory pixel based upon the determinedbrightness value, determine a weight value of the initial pixelaccording to the determined weight value of the compensatory pixel,perform a weighted averaging to obtain a synthesized pixel componentvalue for each of the pixel components based on the weight value and thepixel component value of the pixel component of the initial pixel andthe weight value and the pixel component value of the pixel component ofthe compensatory pixel, and determine the synthesized pixel value basedupon the obtained synthesized pixel component value for each of thepixel components

Also in accordance with the present disclosure, there is provided acamera including an image capturing device configured to capture imagesand a processor coupled to the image capturing device and configured tocontrol the image capturing device to capture an initial image of asubject based on a preset initial exposure value, control the imagecapturing device to capture a compensatory image of the subject based ona preset compensatory exposure values greater than the initial exposurevalue, calculate a synthesized pixel value at a pixel coordinateposition based on a pixel value of an initial pixel at the pixelcoordinate position in the initial image and a pixel value of acompensatory pixel at the pixel coordinate position in the compensatoryimage, and generate a captured image based upon the synthesized pixelvalue.

With the embodiments of the present disclosure, an image captured withan initial exposure value may be compensated on a pixel to pixel basisby synthesizing with one or more images captured with one or more higherexposure values, such that the SNR of the processed image can beeffectively increased and the visibility of detail in, e.g., darkregions of the image can be improved at low costs without the need forequipment upgrading.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a signal-to-noise ratio (SNR) against anexposure value, in accordance with an embodiments of the presentdisclosure;

FIG. 2 is a flowchart of an image processing method, in accordance withan embodiments of the present disclosure;

FIG. 3 is a flowchart of another image processing method, in accordancewith an embodiments of the present disclosure;

FIG. 4 is a flowchart of a method for determining weight values, inaccordance with an embodiments of the present disclosure;

FIG. 5 is a flowchart of another method for determining weight values,in accordance with an embodiments of the present disclosure;

FIG. 6 is a flowchart of a method for determining a synthesized pixelvalue of a multi-channel image, according to embodiments of the presentdisclosure;

FIG. 7 is a view showing a comparison of images with and without theprocessing in accordance with embodiments of the present disclosure;

FIG. 8 is a schematic view of an image processing device, in accordancewith an embodiments of the present disclosure;

FIG. 9 is a schematic view showing a configuration of the processingmodule in FIG. 8, in accordance with an embodiment of the presentdisclosure;

FIG. 10 is a schematic view showing another configuration of theprocessing module in FIG. 8, in accordance with an embodiment of thepresent disclosure; and

FIG. 11 is a schematic view showing a structure of a camera, inaccordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

The technical solutions of the present disclosure will be described withreference to the following embodiments in conjunction with the drawings.The described embodiments are merely illustrative embodiments of thepresent disclosure. Other embodiments will be apparent to those skilledin the art without departing from the disclosure.

In some embodiments of the present disclosure, an image captured with aninitial exposure value may be compensated on a pixel to pixel basis bysynthesizing with one or more images captured with higher exposurevalues. As shown in FIG. 1, an image having a higher exposure value Evmay have a higher signal-to-noise ratio (SNR). Therefore, the SNR of animage can be effectively increased by fusing an image having a normalexposure value and an image having a higher exposure value. In FIG. 1,the horizontal axis represents the exposure value Ev, and the verticalaxis represents the signal-to-noise ratio SNR.

FIG. 2 is a flowchart of an image processing method, in accordance withan embodiment of the present disclosure. The method can be implementedin various types of cameras. As shown in FIG. 2, at S101, a subject isphotographed with a preset initial exposure value to obtain an initialimage.

An exposure value is a parameter that represents the degree of exposure.The exposure value can be collectively determined by, for example, ashutter speed (an exposure interval), an aperture value, and asensitivity (i.e., ISO value), set in a camera. A brighter image can beobtained with a greater exposure value. The initial exposure value canbe an exposure value manually set by a user based on current ambientlight. Alternatively, the initial exposure value can be a defaultexposure value set in the camera. When the user photographs the subject,the initial image of the subject can be captured based on the initialexposure value.

At S102, the subject is photographed with one or more presetcompensatory exposure values that are greater than the initial exposurevalue to obtain one or more compensatory images corresponding to the oneor more compensatory exposure values.

In some embodiments, one compensatory image can be captured for each ofthe one or more compensatory exposure values. Each of the one or morecompensatory exposure values can be greater than the initial exposurevalue, such that one or more compensatory images that are brighter thanthe initial image can be obtained. An exposure value greater than anormal exposure value is also referred to as an “overexposure value.” Animage captured with an overexposure value is also referred to as an“overexposed image.” The one or more compensatory images can include aplurality of overexposed images.

The process of capturing the one or more compensatory images describedabove and processes described below in S103-S104 can be performed in ashort period of time after the process of S101 to obtain a final image.

At S103, a synthesized pixel value of a pixel in the final image iscalculated using a pixel value of a corresponding pixel in the initialimage and a pixel value of a corresponding pixel in each of the one ormore compensatory images. In the present disclosure, a pixel in theinitial image is also referred to as an “initial pixel,” a pixel in acompensatory image is also referred to as a “compensatory pixel,” and apixel in the final image is also referred to as a “final pixel.”

In some embodiments, the synthesized pixel value of a pixel can becalculated by averaging the pixel values of pixels that have a samepixel coordinate position in the initial image and each of the one ormore compensatory images.

In some embodiments, weight values can be assigned to pixels in the oneor more compensatory images based on the pixel values of the pixels inthe one or more compensatory images. Further, weight values can also beassigned to pixels in the initial image. In these embodiments, thesynthesized pixel value of a pixel at a pixel coordinate position can becalculated as a weighted average of the pixels values using thedetermined weight values. In some embodiments, the pixels in the one ormore compensatory images, which may be overexposed images, can beclassified. For example, for a compensatory pixel, a high weight valuecan be assigned if the compensatory pixel is a normally exposed pixeland a low weight value or a zero weight value can be assigned if thecompensatory pixel is an overexposed pixel. An image having a better SNRcan be obtained by weighted averaging pixels having the same pixelcoordinate position in the initial image and each of the one or morecompensatory images.

At S104, the final image is generated based on the calculatedsynthesized pixel values of the final pixels at respective positions.

That is, a complete image, i.e., the final image, can be generated as acaptured image from the calculated synthesized pixel values of the finalpixels at respective pixel coordinate positions.

It should be noted that images, e.g., the initial image and the one ormore compensatory images, processed according to the above-describedexemplary method are brightness images, i.e., grayscale images. In someembodiments, one or more of the initial image and the one or morecompensatory images can be multi-channel images such as RGB images. Inthese embodiments, RGB components in the one or more multi-channelimages can be converted into brightness values according to conversioncoefficients stipulated in ITU-709, and then the method discussed abovecan be performed.

In some embodiments of the present disclosure, an image captured with aninitial exposure value may be compensated on a pixel to pixel basis bysynthesizing with one or more images captured with one or more higherexposure values, such that the SNR of a final image can be effectivelyincreased and the visibility of detail in a dark region of the finalimage can be improved at low costs without the need for equipmentupgrading.

FIG. 3 is a flowchart of another image processing method, in accordancewith an embodiments of the present disclosure. The method can beimplemented in various types of cameras. As shown in FIG. 3, at S201, inthe process of photographing a subject, the subject is photographedusing a preset initial exposure value to obtain an initial image.

An exposure value is a parameter that represents the degree of exposure.The exposure value can be collectively determined by, for example, ashutter speed (an exposure interval), an aperture value, and asensitivity (i.e., ISO value), set in a camera. A brighter image can beobtained with a greater exposure value. The initial exposure value canbe an exposure value manually set by a user based on current ambientlight. Alternatively, the initial exposure value can be a defaultexposure value set in the camera. When the user photographs the subject,the initial image of the subject can be captured based on the initialexposure value.

At S202, the subject is photographed using one or more presetcompensatory exposure values that are greater than the initial exposurevalue to obtain one or more compensatory images corresponding to the oneor more compensatory exposure values.

In some embodiments, a compensatory image can be captured for each ofthe one or more compensatory exposure values. Each of the one or morecompensatory exposure values can be greater than the initial exposurevalue, such that one or more images that are brighter than the initialimage can be obtained. The one or more compensatory images can include aplurality of overexposed images captured based on the one or morecompensatory exposure values, e.g., one or more overexposure values.

At S203, weight values for pixels of the initial image and weight valuesfor pixels of the one or more compensatory images are determined.

At S204, for each pixel position, a weighted average of a pixel value ofa pixel at that pixel position in the initial image and a pixel value ofa corresponding compensatory pixel at that pixel position in each of theone or more compensatory images is calculated considering the weightvalues of the pixels at that pixel position in the initial image and theone or more compensatory images, to calculate a synthesized pixel valueof a corresponding pixel at that pixel position in the final image.

In some embodiments, a sum of the weight values for corresponding pixelsat a same pixel coordinate position in the initial image and the one ormore compensatory images is 1. Therefore, the weight value for a pixelof the initial image can be calculated when the weight value for thecorresponding compensatory pixel in each of the one or more compensatoryimages is determined, where the weight value for a compensatory pixel ina compensatory image can be calculated based on the pixel value of thispixel.

For example, assume K compensatory images are captured. One approach forcalculating the synthesized pixel value of a final pixel can includefirst calculating a weighted average of the pixel value of acorresponding initial pixel and the pixel value of a correspondingcompensatory pixel for each of the K compensatory images to obtain Kweighted averages, and then calculating an average of the K weightedaverages as the synthesized pixel value of the final pixel. Thisapproach is described in more detail below.

First, a preliminary weight value of a compensatory pixel at a pixelcoordinate position in a k-th compensatory image of the K compensatoryimages is determined. Specifically, a variable ω_(k) can be determinedbased on the pixel value of this compensatory pixel, whereinω_(k)∈[0,1]. For example, a larger value can be assigned to the variableω_(k) for a compensatory pixel having a greater pixel value. Afterdetermining the variable ω_(k), the preliminary weight value of thecompensatory pixel at the pixel coordinate position in the k-thcompensatory image can be determined as 1−Ω_(k), and the preliminaryweight value of the corresponding initial pixel at the pixel coordinateposition in the initial image can be determined as 1−(1−ω_(k)), i.e.,ω_(k).

Based on the above determined weight values, the synthesized pixel valueof the final pixel at the pixel coordinate position can be calculatedusing the following equation:

$\begin{matrix}{\overset{\_}{p} = {\frac{1}{K}{\sum\limits_{k = 1}^{K}\left( {{\omega_{k}P_{0}} + {\left( {1 - \omega_{k}} \right)P_{k}}} \right)}}} & (1)\end{matrix}$wherein P₀ is the pixel value of the initial pixel at the pixelcoordinate position in the initial image, P_(k) is the pixel value ofthe compensatory pixel at the same pixel coordinate position in the k-thcompensatory image, and p is the weighted average of the pixel values ofall pixels at the same corresponding pixel coordinate position in theinitial image and the one or more compensatory images. As can be seenfrom Equation (1), an overall weight value, i.e., the “weight value”referred to above in, e.g., S203, of the compensatory pixel in the k-thcompensatory image as in the final weighted averaging calculation (e.g.,Equation (1)) is

$\frac{1 - \omega_{k}}{K},$and the overall weight value of the corresponding initial pixel as inthe final weighted averaging calculation is

$\frac{1}{K}{\sum\limits_{k = 1}^{K}{\omega_{k}.}}$When k=1, the problem reduces to the situation where only onecompensatory image is captured, in which the preliminary weight valueand the overall weight value of a pixel are identical. In the presentdisclosure, unless otherwise specified, the term “weight value” alonerefers to the overall weight value.

At S205, the final image is generated based on the calculatedsynthesized pixel values of the final pixels at respective positions.

That is, a complete image, i.e., the final image, can be generated as acaptured image from the calculated synthesized pixel values of the finalpixels at respective pixel coordinate positions.

The process of determining weight values in S203 can be performed by amethod illustrated in FIG. 4. FIG. 4 is a flowchart of a method fordetermining weight values, in accordance with an embodiments of thepresent disclosure. As shown in FIG. 4, at S301, the pixel values of thecompensatory pixels in the one or more compensatory images are detected.

In some embodiments of the present disclosure, the pixel value of apixel can be represented by a brightness value ranging from 0 to 255.According to the disclosure, each of the one or more compensatory imagescan be an overexposed image captured based on a compensatory exposurevalue corresponding to an overexposure value. Such an overexposed imagecan include both overexposed pixels and pixels having a large exposurevalue but not being overexposed.

At S302, the weight values of the compensatory pixels in the one or morecompensatory images are determined, where each of the weight values isin a range from 0 to 1 (both inclusive).

In some embodiments, a weight value for a brightness value can bedetermined by training using a training set including a plurality ofimages. A mapping table of brightness values and corresponding weightvalues can be generated, such that a weight value corresponding to abrightness value in a compensatory image can be determined by searchingthe mapping table. In some embodiments, a variable for a compensatorypixel can be first determined, and then a weight value of thecompensatory pixel in a compensatory image can be determined accordingto the variable. This approach of determining the weight value is simpleand accurate with relatively small processing overhead.

At S303, the weight values of the initial pixels in the initial imageare determined based upon the determined weight values for thecompensatory pixels in the one or more compensatory images.

In some embodiments of the present disclosure, in the process ofdetermining the weight value of a compensatory pixel at a correspondingpixel coordinate position in the k-th compensatory image, a variableω_(k) can be first determined based upon the pixel value of thiscompensatory pixel, wherein ω_(k)∈[0,1] and ω_(k) is larger for acompensatory pixel having a greater pixel value. After determining thevariable ω_(k), the preliminary weight value of the compensatory pixelat the pixel coordinate position in the k-th compensatory image iscalculated as 1−ω_(k), and the preliminary weight value of the initialpixel at the same pixel coordinate position in the initial image isω_(k). Correspondingly, the overall weight value of the compensatorypixel in the k-th compensatory image and that of the correspondinginitial pixel at the pixel coordinate position are

${\frac{1 - \omega_{k}}{K}\mspace{14mu}{and}\mspace{14mu}\frac{1}{K}{\sum\limits_{k = 1}^{K}\omega_{k}}},$respectively.

FIG. 5 shows a flowchart of a method of determining the weight values inS203 according to another embodiment of the disclosure. As shown in FIG.5, at S401, the pixel values of the compensatory pixels in the one ormore compensatory images are detected.

In some embodiments of present disclosure, the pixel value of the pixelcan be represented as a brightness value ranging from 0 to 255.

At S402, variables corresponding to the compensatory pixels in the oneor more compensatory images are determined. Specifically, for acompensatory pixel having a pixel value smaller than a preset threshold,the corresponding variable is determined as having a value 0. On theother hand, for a compensatory pixel having a pixel value equal to orgreater than the preset threshold, the corresponding variable isdetermined as having a value 1.

At S403, a binary image is generated for each of the one or morecompensatory images based on the determined variable values. In someembodiments, a smooth filtering is performed on the generated one ormore binary images.

At S404, the weight values of the compensatory pixels in the one or morecompensatory images and the weight values of the initial pixels in theinitial image are determined according to the variable values of pointsin the binary images.

In some embodiments of present disclosure, a classification of pixelscan be performed based on the pixel values of the compensatory pixels inthe one or more compensatory images. For instance, for a compensatorypixel having a pixel value of p_(k+1) in the k-th compensatory image,the value of the corresponding variable ω_(k) can be determined by:

$\begin{matrix}{\omega_{k} = \left\{ \begin{matrix}{0,} & {p_{k} < T} \\{1,} & {p_{k} \geq T}\end{matrix} \right.} & (2)\end{matrix}$wherein T is a threshold for determining whether a pixel is saturated.The threshold T can have a value ranging from 230 to 255. A binary imageW_(k) corresponding to the k-th compensatory image can be obtained fromEquation (2), in which the value ω_(k) of each pixel is 1 or 0,indicating whether the corresponding compensatory pixel in thecompensatory image is overexposed or not. A smooth filtering, such as aGaussian filtering, may be performed to the binary image W_(k) toprevent a significant change around those saturated pixels in the image.

In the filtered binary image W_(k), the value of variable ω_(k) of eachpixel is within a range from 0 to 1, both inclusive. It is noted that inthe filtered binary image, the value of a variable is not necessarily 0or 1 due to the smooth filtering. The preliminary weight value of thecorresponding compensatory pixel in the compensatory image correspondingto the filtered binary image is 1−ω_(k), and the preliminary weightvalue of the corresponding initial pixel in the initial image is ω_(k).The overall weight values of the corresponding compensatory pixel andthe initial pixel are

${\frac{1 - \omega_{k}}{K}\mspace{14mu}{and}\mspace{14mu}\frac{1}{K}{\sum\limits_{k = 1}^{K}\omega_{k}}},$respectively.

FIG. 6 is a flowchart of a method for determining synthesized pixelvalues of a multi-channel image, according to the embodiments of thepresent disclosure. In these embodiments, each of the initial image andthe one or more compensatory images can be a triple-channel image, suchas an RGB image. As shown in FIG. 6, at S501, if the one or morecompensatory images are one or more multi-channel images having multiplechannels, a brightness value conversion is performed based on (1) presetconversion coefficients and (2) pixel component values of respectivecompensatory pixels in the one or more compensatory images, to obtainbrightness values of respective compensatory pixels. For eachcompensatory pixel, a pixel component value corresponds to one of themultiple channels.

At S502, weight values of respective compensatory pixels in the one ormore compensatory images are determined based on the determinedbrightness values of the respective compensatory pixels, and the weightvalues of respective initial pixels in the initial image are determinedbased on the determined weight values of the corresponding compensatorypixels.

A multi-channel image may be, for example, an RGB image. An RGB imagecan produce various colors by changing and adding the three colorchannels of three pixel components, i.e., red (R), green (G), and blue(B), in various manners. The conversion coefficients can be theconversion coefficients as stipulated by ITU-709. Brightness values ofrespective pixels can be calculated from the corresponding RGBcomponents, and then the weight values of the respective pixels can becalculated using the method described above with reference to FIG. 4 orFIG. 5. For example, an equation for calculating a brightness value Yfrom the RGB components can be: Y=0.30*R+0.59*G+0.11*B.

At S503, a weighted averaging is performed based on (1) the weight valueand the pixel component values of an initial pixel at a pixel coordinateposition in the initial image, and (2) the weight value and the pixelcomponent values of each corresponding compensatory pixel in the one ormore compensatory images, to obtain a weighted average of each pixelcomponent at the pixel coordinate position for the final image.

That is, the weighted average of R, the weighted average of G, and theweighted average of B at a pixel coordinate position can be calculatedfrom the RGB components of the pixels (including the initial pixels andone or more compensatory pixels) at the pixel coordinate position andthe determined weight values of the pixels at the pixel coordinateposition.

At S504, synthesized pixel values at respective pixel coordinatepositions are determined based upon the weighted averages.

The synthesized pixel value of each compensated pixel can be obtained bycombining the weighted averages of the corresponding channel components.For example, for a pixel, if the weighted averages of R, G, and B are124, 205, and 124, respectively, a synthesized pixel value is #7CCD7C(hexadecimal). Once the synthesized pixel value is determined, an SNR ofthe initial image can be increased based upon the synthesized pixelvalue.

FIG. 7 is a view showing a comparison of images, in accordance with anembodiment of the present disclosure. The image in the upper panel ofFIG. 7 is captured with a normal exposure value of a scene with dimmedenvironmental light, in which a certain region, as indicated by thecircle, is dark and contains less discernable details due toinsufficient illumination. The lower panel of FIG. 7 shows an imageobtained according to the present disclosure by processing the image inthe upper panel of FIG. 7 using one or more images captured under one ormore higher exposure values (overexposure). As shown in FIG. 7, in theprocessed image, the visibility of details in the dark region isimproved, and the SNR of the dark region is increased. A quality of theentire image is improved and a greater dynamic range is obtained.

In some embodiments of the present disclosure, an image captured underan initial exposure value may be compensated on a pixel to pixel basisby weighted averaging with one or more images captured under one or morehigher exposure values. The SNR of the processed image can beeffectively increased, and a visibility of details in, e.g., darkregions can be improved at low a cost, without the need for equipmentupgrade.

An image processing device and a camera according to embodiments of thepresent disclosure will be described in detail below.

FIG. 8 is a schematic view of an image processing device, in accordancewith an embodiments of the present disclosure. The image processingdevice shown in FIG. 8 can be provided in various types of cameras andincludes a capturing module 1, a processing module 2, and a generatingmodule 3.

The capturing module 1 can be configured to photograph a subject with apreset initial exposure value to obtain an initial image and photographthe subject with one or more preset compensatory exposure values thatare greater than the initial exposure value to obtain one or morecompensatory images.

The processing module 2 can be configured to perform a calculation usingpixel values of initial pixels at respective positions in the initialimage and pixel values of compensatory pixels at corresponding positionsin the one or more compensatory images to obtain synthesized pixelvalues of final pixels at the respective positions in a final image.

The generating module 3 can be configured to generate a captured image,i.e., the final image, based upon the synthesized pixel values of thefinal pixels at the respective positions.

The initial exposure value and the one or more compensatory exposurevalues can be pre-stored in a memory. The capturing module 1 can capturethe initial image and the compensatory images with the exposure valuesstored in the memory. An exposure value is a parameter that representsthe degree of exposure, and can be collectively determined by a shutterspeed (an exposure interval), an aperture value, and a sensitivity(i.e., ISO value), set in a camera. A brighter image can be obtainedwith a greater exposure value.

The initial exposure value can be an exposure value manually set by auser based on current ambient light. Alternatively, the initial exposurevalue can be a default exposure value set in the camera. When the userphotographs the subject, the initial image of the subject can becaptured based on the initial exposure value.

In some embodiments, one compensatory image can be captured for each ofthe one or more compensatory exposure values. Each of the one or morecompensatory exposure values can be greater than the initial exposurevalue, such that one or more compensatory images that are brighter thanthe initial image can be obtained. The one or more compensatory imagescan include a plurality of overexposed images captured based on the oneor more compensatory exposure values corresponding to overexposurevalues. It should be noted that in the overexposed images, there mayhave overexposed pixels and pixels with large exposure but notoverexposed.

In some embodiments, the processing module 2 calculates the synthesizedpixel value by averaging the pixel values of pixels that have a samepixel coordinate position in the initial image and each of the one ormore compensatory images.

In some embodiments, the processing module 2 calculates the synthesizedpixel value by determining weight values for pixels in the one or morecompensatory images and pixels in the initial image based on the pixelvalues of the compensatory pixels, and performing a weighted averagebased on the determined weight values to obtain a synthesized pixelvalue of a pixel at a pixel coordinate position. According to actualrequirements on image quality, the pixels in the one or morecompensatory images, which may be overexposed images, can be classified.For example, a high weight value can be assigned to a normally exposedcompensatory pixel, and a low weight value or a zero weight value can beassigned to an overexposed compensatory pixel. An image having a betterSNR can be obtained by weighted averaging pixels having the same pixelcoordinate position in the initial image and each of the one or morecompensatory images.

The generating module 3 can generate a complete image as a capturedimage from the calculated synthesized pixel values of the final pixelsat respective pixel coordinate positions as calculated by the processingmodule 2.

FIG. 9 is a schematic view showing a configuration of the processingmodule 2 in FIG. 8, in accordance with an embodiment of the presentdisclosure. The processing module 2 shown in FIG. 9 includes aprocessing unit 21 and a calculating unit 22.

The processing unit 21 can be configured to determine a weight value foreach pixel of the initial image and a weight value for each pixel of theone or more compensatory images.

The calculating unit 22 can be configured to perform a weightedaveraging based on (1) a pixel value of an initial pixel at eachposition in the initial image and the weight value thereof, and (2) apixel value of a compensatory pixel at a corresponding position in eachof the one or more compensatory images and the weight value thereof, tocalculate a synthesized pixel value of the final pixel at thecorresponding position in the final image.

In some embodiments, the processing unit 21 is configured to detect thepixel values of respective compensatory pixels in the one or morecompensatory images, determine weight values of the respectivecompensatory pixels in the one or more compensatory images each as avalue ranging from 0 to 1, and determine weight values of respectiveinitial pixels in the initial image based upon the determined weightvalues for the compensatory pixels in the one or more compensatoryimages.

In some embodiments, the processing unit 21 is configured to (1) detectpixel values of respective compensatory pixels in the one or morecompensatory images; (2) determine a variable corresponding to acompensatory pixel having a pixel value no less than a preset thresholdas having a value 1, and determine the variable corresponding to acompensatory pixel having a pixel value less than the preset thresholdas having a value 0; (3) generate a binary image for each of the one ormore compensatory images based upon the determined variables, performsmooth filtering on the generated one or more binary images; and (4)determine the weight values of respective compensatory pixels in each ofthe one or more compensatory images according to the values of variablesin a corresponding smooth filtered binary images, and determine theweight values of respective initial pixels in the initial image.

In some embodiments, the processing unit 21 is configured to determine,if the one or more compensatory images are one or more multi-channelimages, the weight values of respective compensatory pixels based uponcomponent values of the compensatory pixels corresponding to thechannels of the one or more compensatory images and correspondingthresholds, and determine the weight values of respective initial pixelsin the initial image based upon the weight values of correspondingcompensatory pixels in the one or more compensatory images.

The processing unit 21 can determine the weight values as describedhereinabove. The specific process is described hereinabove in theembodiments of the present disclosure.

It should be noted that the processing unit 21 and the calculating unit22 can perform calculation on brightness images (i.e., grayscaleimages). If the initial image and the one or more compensatory imagesare multi-channel images such as RGB images, the processing module 2 canperform the above discussed process after corresponding RGB componentsare converted to brightness values according to conversion coefficientsstipulated in ITU-709. FIG. 10 is a schematic view showing anotherconfiguration of the processing module 2 in FIG. 8, in accordance withan embodiment of the present disclosure. The processing module 2 shownin FIG. 10 according to the embodiments of the present disclosureincludes a component processing unit 23 and a component calculating unit24.

The component processing unit 23 can be configured to perform, if theone or more compensatory images are one or more multi-channel imageseach including a plurality of pixel component values, a brightness valueconversion based on (1) preset conversion coefficients and (2) pixelcomponent values of each compensatory pixel in the compensatory images,to obtain a brightness value of each compensatory pixel.

The component calculating unit 24 can be configured to (1) determine theweight values of respective compensatory pixels in the one or morecompensatory images based on the determined brightness values of therespective compensatory pixels, and determine the weight values ofrespective initial pixels in the initial image based on the determinedweight values of the corresponding compensatory pixels; (2) perform aweighted averaging based on (a) the weight value and the pixel componentvalues of each initial pixel in the initial image, and (b) the weightvalue and the pixel component values of each corresponding compensatorypixel in the one or more compensatory images, to obtain a synthesizedvalue of each pixel component of each corresponding final pixel; and (3)determine the synthesized pixel value of each final pixel based upon theobtained synthesized values of the pixel components.

In some embodiments, the processing module 2 can include the processingunit 21, the calculating unit 22, the component processing unit 23, andthe component calculating unit 24 as discussed hereinabove, so as toprocess different types of images. Each of the units can be implementedwith reference to FIG. 2 to FIG. 6.

In some embodiments of the present disclosure, an image captured underan initial exposure value may be compensated on a pixel to pixel basisby weighted averaging with one or more images captured under one or morehigher exposure values. The SNR of the processed image can beeffectively increased, and a visibility of details in, e.g., darkregions can be improved at a low cost, without the need for equipmentupgrading.

Furthermore, the above discussed methods of assigning weight values forthe compensatory images, such as the methods based on the mapping tableof weight values and pixel values, are simple and accurate with arelatively small processing overhead. The methods of determining weightvalues by performing smooth filtering on binary images may obtain animage having higher SNR while effectively preventing a significantchange around the saturated pixels in a compensatory image.

FIG. 11 is a schematic view showing a structure of a camera, inaccordance with an embodiment of the present disclosure. The camerashown in FIG. 11 includes an image capturing device 100 and a processor200.

The image capturing device 100 can be configured to capture images of asubject under a control of the processor 200.

The processor 200 can be configured to (1) control the image capturingdevice 100 to photograph the subject with a preset initial exposurevalue to obtain an initial image; (2) control the image capturing device100 to photograph the subject with one or more preset compensatoryexposure values that are greater than the initial exposure value toobtain one or more compensatory images; (3) calculate a synthesizedpixel value of each pixel in a final image from a pixel value of acorresponding initial pixel in the initial image and a pixel value of acorresponding pixel in each of the one or more compensatory images; and(4) generate a captured image, i.e., the final image, based upon thesynthesized pixel value of each final pixel.

The initial exposure value and the compensatory exposure values can bepre-stored in a memory. The processor 200 can capture the initial imageand the one or more compensatory images with the exposure values storedin the memory. An exposure value is a parameter that represents thedegree of exposure, and can be collectively determined by a shutterspeed (an exposure interval), an aperture value, and a sensitivity(i.e., ISO value), set in the camera. A brighter image can be obtainedwith a greater exposure value.

The initial exposure value can be an exposure value manually set by auser based on the current ambient light. Alternatively, the initialexposure value can be a default exposure value set in the camera. Whenthe user photographs a subject, the initial image of the subject can becaptured based on the initial exposure value.

The processor 200 can instruct the image capturing device 100 to captureone compensatory image based upon each one of the one or morecompensatory exposure values. Each of the one or more compensatoryexposure values can be greater than the initial exposure value, suchthat one or more images that are brighter than the initial image can beobtained. The one or more compensatory images can include a plurality ofoverexposed images captured based on the one or more compensatoryexposure values, e.g., one or more overexposure values. It should benoted that an overexposed image may include overexposed pixels andpixels with large exposure but not overexposed.

In some embodiments, the processor 200 calculates the synthesized pixelvalue by averaging the pixel values of pixels that have the same pixelcoordinate position in the initial image and each of the one or morecompensatory images.

Alternatively, the processor 200 calculates the synthesized pixel valueby determining weight values for compensatory pixels in the one or morecompensatory images and initial pixels in the initial image based on thepixel values of the compensatory pixels, and performing a weightedaveraging based on the determined weight values to obtain a synthesizedpixel value of a final pixel at a pixel coordinate position. Accordingto actual requirements on image quality, the compensatory pixels in theone or more compensatory images, i.e., one or more overexposed images,can be classified. For example, a high weight value can be assigned to anormally exposed compensatory pixel, and a low weight value or a zeroweight value can be assigned to an overexposed compensatory pixel. Animage having a better SNR can be obtained by weighted averaging pixelsthat have the same pixel coordinate positions in the initial image andeach of the one or more compensatory images.

The processor 200 can generate a complete image, i.e., the final image,as a captured image from the calculated synthesized pixel value of eachof the final pixels at respective pixel coordinate positions.

It should be noted that the above exemplary method is performed onbrightness images, i.e., grayscale images. If the initial image and theone or more compensatory images are multi-channel images such as RGBimages, the processor 200 can perform the above described process aftercorresponding RGB components are converted to brightness valuesaccording to conversion coefficients stipulated in ITU-709.

In some embodiments, when calculating a synthesized pixel value of eachfinal pixel in the final image from a pixel value of the correspondingpixel at a corresponding position in the initial image and a pixel valueof the corresponding compensatory pixel at a corresponding position ineach of the one or more compensatory images, the processor 200 (1)determines a weight value for the corresponding initial pixel of theinitial image and a weight value for the corresponding compensatorypixel of each of the one or more compensatory images, and (2) performs aweighted averaging based on (a) the pixel value of the correspondinginitial pixel in the initial image and the weight value thereof, and (b)the pixel value of the corresponding compensatory pixel in each of theone or more compensatory images and the weight value thereof, tocalculate the synthesized pixel value of the final pixel.

In some embodiments, when determining a weight value for an initialpixel of the initial image and a weight value for a correspondingcompensatory pixel of each of the one or more compensatory images, theprocessor 200 (1) detects a pixel value of the compensatory pixel ineach of the one or more compensatory images; (2) determines the weightvalue of the compensatory pixel in each of the one or more compensatoryimages as a value ranging from 0 to 1; and (3) determines the weightvalue of the initial pixel in the initial image based upon thedetermined weight value for the compensatory pixel in each of the one ormore compensatory images.

In some embodiments, when determining the weight value for each initialpixel of the initial image and the weight value for the correspondingcompensatory pixel of each of the one or more compensatory images, theprocessor 200 (1) detects pixel values of respective compensatory pixelsin the one or more compensatory images; (2) determines a variablecorresponding to a compensatory pixel having a pixel value no less thana preset threshold as having a value 1, and determine the variablecorresponding to a compensatory pixel having a pixel value less than thepreset threshold as having a value 0; (3) generates a binary image foreach of the one or more compensatory images based upon the determinedvariables, performs a smooth filtering on the generated one or morebinary images; and (4) determines the weight values of respectivecompensatory pixels in each of the one or more compensatory imagesaccording to the values of variables in a corresponding smooth filteredbinary images, and determines the weight values of respective initialpixels in the initial image.

In some embodiments, when calculating the synthesized pixel value ofeach final pixel from the pixel value of the corresponding initial pixelin the initial image and the pixel value of the correspondingcompensatory pixel in each of the one or more compensatory images, ifthe one or more compensatory images are one or more multi-channel imagesin which each compensatory pixel has a plurality of pixel componentvalues, then the processor 200 (1) performs a brightness valueconversion based on (a) preset conversion coefficients and (b) pixelcomponent values of respective compensatory pixels in the one or morecompensatory images, to obtain brightness values of respectivecompensatory pixels; (2) determines the weight values of thecompensatory pixels in each of the one or more compensatory images basedupon the determined brightness values of respective compensatory pixels,and determines the weight values of the initial pixels in the initialimage; (3) performs a weighted averaging based on (a) the weight valueand the pixel component values of each initial pixel in the initialimage, and (b) the weight value and the pixel component values of eachcorresponding compensatory pixel in each of the one or more compensatoryimages, to obtain a synthesized value of each pixel component of eachfinal pixel in the final image; and (4) determine the synthesized pixelvalue of each final pixel based upon the obtained synthesized values.

The processor 200 can be implemented according to the embodimentsdescribed with reference to FIG. 2 to FIG. 10.

In some embodiments, the camera shown in FIG. 11 can also include amemory storing instructions that, when executed by the processor 200,cause the processor 200 to perform a method consistent with the presentdisclosure, such as one of the exemplary methods described above. Thememory can be a non-transitory computer-readable storage medium, such asa flash disk, a removable hard drive, a read only memory (ROM), a randomaccess memory (RAM), a magnetic disk, or an optical disk.

In some embodiments, there is also provided an image processing deviceincluding a processor and a memory storing instructions that, whenexecuted by the processor, cause the processor to perform a methodconsistent with the present disclosure, such as one of the exemplarymethods described above. The memory can be a non-transitorycomputer-readable storage medium, such as a flash disk, a removable harddrive, a read only memory (ROM), a random access memory (RAM), amagnetic disk, or an optical disk.

In some embodiments of the present disclosure, an image captured underan initial exposure value may be compensated on a pixel to pixel basisby weighted averaging with one or more images captured under one or morehigher exposure values. The SNR of the processed image can beeffectively increased, and a visibility of details in, e.g., darkregions can be improved at a low cost, without the need for equipmentupgrading.

While embodiments of the present disclosure have been shown anddescribed herein, it will be obvious to those skilled in the art thatsuch embodiments are provided by way of example only. Numerousvariations, changes, and substitutions to the devices and methods willnow occur to those skilled in the art without departing from thedisclosure. For example, the division of modules or units is merely adivision based on logical functionality, and other division is possiblein the actual implementation. For example, a plurality of units orcomponents can be combined or integrated into another system, or somefeatures may be omitted or may not be implemented. Furthermore, a directcoupling or communication connection shown or discussed hereinabove canbe replaced by an indirect coupling or communication connection viainterfaces, devices or units, and may be in the form of electrical,mechanical or other coupling or communication connections.

The units illustrated as separate parts may or may not be physicallyseparated. The components shown as units may or may not be physicalunits, i.e., the components may be provided at one location ordistributed over a plurality of network locations. Portions or all ofthe units can be selected to implement the embodiments in view of actualneeds.

In addition, various functional units of the embodiments of the presentdisclosure can be integrated in one processing unit, or provided asindividual units, or two or more functional units being integrated inone unit. The integrated unit can be implemented in the form of hardwareor software functional unit.

The integrated units can be stored in a computing readable storagemedium if they are implemented in the form of a software functional unitand sold or used as a separate product. Based on this understanding, theportion of the technical solution of the present disclosuresubstantially contributing to the conventional technologies, or portionsor the entirety of the technical solution, can be embodied in the formof a software product which is stored in a storage medium. The softwareproduct can comprise executable instructions causing a computerprocessor to execute all or part of the method according to variousembodiments of the present disclosure. The storage medium may comprisevarious mediums such as a flash disk, a removable hard drive, a readonly memory (ROM), a random access memory (RAM), a magnetic disk or anoptical disk that are capable of storing program codes.

The disclosure herein is merely illustrative of the embodiments of thepresent disclosure with no intention to limit the scope thereof. Anyequivalent structure or flowcharts made in accordance with thedisclosure of the specification and the drawings may be directly orindirectly applied to other related technical fields, and those changesshall also fall within the scope of the present disclosure.

What is claimed is:
 1. An image processing method comprising: capturingan initial image of a subject based on a preset initial exposure value;capturing a plurality of compensatory images of the subject based on aplurality of preset compensatory exposure values greater than theinitial exposure value; calculating a synthesized pixel value at a pixelcoordinate position based on a pixel value of an initial pixel at thepixel coordinate position in the initial image and a pixel value of acompensatory pixel at the pixel coordinate position in the eachcompensatory image, wherein calculating the synthesized pixel valuecomprises: for each compensatory image, determining a weight value ofthe initial pixel and a weight value of the compensatory pixel based ona mapping table of brightness values and corresponding weight values, aweight value for a brightness value being determined by training using atraining set including a plurality of images; generating a plurality ofpreliminary synthesized pixels having a one-to-one correspondence withthe plurality of compensatory images, wherein for each compensatoryimage, the corresponding preliminary synthesized pixel is calculated byperforming a weighted averaging to calculate the synthesized pixel valuebased on the pixel value and the weight value of the initial pixel andthe pixel value and the weight value of the compensatory pixel;calculating the synthesized pixel value as an average of the pluralityof preliminary synthesized pixels; and generating a captured image basedupon the synthesized pixel value.
 2. The method of claim 1, wherein theweight value of the compensatory pixel ranges from 0 to
 1. 3. The methodof claim 1, further comprising: performing a smooth filtering on theweight value of the compensatory pixel and the weight value of theinitial pixel.
 4. The method of claim 1, wherein: the initial image andthe plurality of compensatory images are multi-channel images eachhaving a plurality of pixel components for each pixel, and calculatingthe preliminary synthesized pixel value includes: performing abrightness value conversion based on preset conversion coefficients andpixel component values of the compensatory pixel to obtain a brightnessvalue of the compensatory pixel; determining the weight value of thecompensatory pixel based upon the determined brightness value;determining the weight value of the initial pixel according to thedetermined weight value of the compensatory pixel; performing a weightedaveraging to obtain a preliminary synthesized pixel component value foreach of the pixel components based on: the weight value and the pixelcomponent value of the pixel component of the initial pixel, and theweight value and the pixel component value of the pixel component of thecompensatory pixel; and determining the preliminary synthesized pixelvalue based upon the obtained preliminary synthesized pixel componentvalue for each of the pixel components.
 5. A device comprising: aprocessor; and a memory storing instructions that, when executed by theprocessor, cause the processor to: obtain an initial image of a subjectcaptured based on a preset initial exposure value; obtain a plurality ofcompensatory images of the subject captured based on a plurality ofpreset compensatory exposure values greater than the initial exposurevalue; calculate a synthesized pixel value at a pixel coordinateposition based on a pixel value of an initial pixel at the pixelcoordinate position in the initial image and a pixel value of acompensatory pixel at the pixel coordinate position in the eachcompensatory image, wherein calculating the synthesized pixel valuecomprises: for each compensatory image, determining a weight value ofthe initial pixel and a weight value of the compensatory pixel based ona mapping table of brightness values and corresponding weight values, aweight value for a brightness value being determined by training using atraining set including a plurality of images; and generating a pluralityof preliminary synthesized pixels having a one-to-one correspondencewith the plurality of compensatory images, wherein for each compensatoryimage, the corresponding preliminary synthesized pixel is calculated byperforming a weighted averaging to calculate the synthesized pixel valuebased on the pixel value and the weight value of the initial pixel andthe pixel value and the weight value of the compensatory pixel;calculating the synthesized pixel value as an average of the pluralityof preliminary synthesized pixels; and generate a captured image basedupon the synthesized pixel value.
 6. The device of claim 5, wherein theinstructions further cause the processor to: perform a smooth filteringon the weight value of the compensatory pixel and the weight value ofthe initial pixel.
 7. The device of claim 5, wherein: the initial imageand the plurality of compensatory images are multi-channel images eachhaving a plurality of pixel components for each pixel, and theinstructions further cause the processor to: perform a brightness valueconversion based on preset conversion coefficients and pixel componentvalues of the compensatory pixel to obtain a brightness value of thecompensatory pixel; determine the weight value of the compensatory pixelbased upon the determined brightness value; determine the weight valueof the initial pixel according to the determined weight value of thecompensatory pixel; perform a weighted averaging to obtain a preliminarysynthesized pixel component value for each of the pixel components basedon: the weight value and the pixel component value of the pixelcomponent of the initial pixel, and the weight value and the pixelcomponent value of the pixel component of the compensatory pixel; anddetermine the preliminary synthesized pixel value based upon theobtained preliminary synthesized pixel component value for each of thepixel components.
 8. A system, comprising: a camera configured tocapture images; and a processor coupled to the camera and configured to:control the camera to capture an initial image of a subject based on apreset initial exposure value; control the camera to capture a pluralityof compensatory images of the subject based on a plurality of presetcompensatory exposure values greater than the initial exposure value;calculate a preliminary synthesized pixel value at a pixel coordinateposition based on a pixel value of an initial pixel at the pixelcoordinate position in the initial image and a pixel value of acompensatory pixel at the pixel coordinate position in the eachcompensatory image, wherein calculating the synthesized pixel valuecomprises: for each compensatory image; determining a weight value ofthe initial pixel and a weight value of the compensatory pixel based ona mapping table of brightness values and corresponding weight values, aweight value for a brightness value being determined by training using atraining set including a plurality of images; and generating a pluralityof preliminary synthesized pixels having a one-to-one correspondencewith the plurality of compensatory images, wherein for each compensatoryimage, the corresponding preliminary synthesized pixel is calculated byperforming a weighted averaging to calculate the synthesized pixel valuebased on the pixel value and the weight value of the initial pixel andthe pixel value and the weight value of the compensatory pixel;calculating the synthesized pixel value as an average of the pluralityof preliminary synthesized pixels; and generate a captured image basedupon the synthesized pixel value.
 9. The system of claim 8, wherein: theprocessor is further configured to perform a smooth filtering on theweight value of the compensatory pixel and the weight value of theinitial pixel.
 10. The system of claim 8, wherein: the initial image andthe plurality of compensatory images are multi-channel images eachhaving a plurality of pixel components for each pixel, and calculatingthe preliminary synthesized pixel value includes: performing abrightness value conversion based on preset conversion coefficients andpixel component values of the compensatory pixel to obtain a brightnessvalue of the compensatory pixel; determining the weight value of thecompensatory pixel based upon the determined brightness value;determining the weight value of the initial pixel according to thedetermined weight value of the compensatory pixel; performing a weightedaveraging to obtain a preliminary synthesized pixel component value foreach of the pixel components based on: the weight value and the pixelcomponent value of the pixel component of the initial pixel, and theweight value and the pixel component value of the pixel component of thecompensatory pixel; and determining the preliminary synthesized pixelvalue based upon the obtained preliminary synthesized pixel componentvalue for each of the pixel components.